The present invention relates to an optical recording device and, more particularly, to an optical recording device that records and reproduces information by charging the periodic structure of a photonic crystal.
In recent years optical devices, called photonic crystals, have come to industry attention as devices that permit microminiature optical integrated circuits (ICs). The photonic crystals have a periodic structure with two kinds of media of different refractive indexes arranged in a repeating cyclic order. The photonic crystals fall roughly into one-dimensional (1-D), two dimensional (2-D) and three-dimensional (3-D) photonic crystals.
The 1-D photonic crystal has heretofore been known as a multi-layer film, and now it finds extensive applications such as a WDM (Wavelength Division Multiplexing) filter and various other devices. The 3-D photonic crystal has a structure formed by a three-dimensional periodic alternation of two kinds of media of different refractive indexes, and it is put to practical use, for example, as a polarization separating element.
The 2-D photonic crystal has a periodic structure in which columnar holes are formed in a high-refractive-index material in a square or triangular lattice pattern, or columnar pillars of a high-refractive-index material are formed in a low-refractive-index material in a square lattice pattern. Such a periodic structure provides a photonic bandgap, which controls in-plane (parallel to the crystal surface) propagation of light incident on the 2-D photonic crystal. By introducing a line crystal defect in the 2-D photonic crystal, an optical waveguide can be formed.
It is described in Japanese Patent Application Kokai Publication No. 2001-272555 (published Oct. 5, 2001, hereinafter referred to as Document 1) that wavelength filtering can be achieved by forming a defect in the photonic crystal near the optical waveguide.
In Japanese Patent Application Kokai Publication No. 2003-36561 (published Feb. 7, 2003, hereinafter referred to as Document 2) there is set forth an application of the photonic crystal to an optical recording device. This example uses the photonic crystal as a polarization separating layer interposed between first and second recording layers of a two-layer optical recording medium.
A typical example of an optical recording device is optical disks, and magneto-optical and phase change optical disks are put to practical use as writable disks. These optical disks are of the type that effects recording and reproduction of information by launching external light into the recording film on the substrate substantially perpendicularly thereto, and information is reproduced by reading reflected light from recorded pits.
Accordingly, in such optical disks there is no optical path in the in-plane direction of the recording film (parallel to the substrate surface), that is, these disks do not use light parallel to the substrate surface. Hence, the recording and reproducing system of such optical disks cannot be applied to an optical recording device integrated with an optical circuit having an optical waveguide in the substrate surface.
On the other hand, as described in Document 1, the 2-D photonic crystal allows the formation of an optical waveguide in the in-plane direction (parallel to the substrate surface), and hence it can be integrated into the optical circuit. In the prior art, however, nothing is disclosed about an optical recording device that uses the 2-D photonic crystal as a writable recording medium. The use of the photonic crystal in the optical recording device is limited only to, for example, separation of light as set forth in Document 2.